Digital data magnetic recording systems store digital data by recording same in a moving magnetic media layer using a storage, or xe2x80x9cwritexe2x80x9d, electrical current-to-magnetic field transducer, or xe2x80x9cheadxe2x80x9d, positioned immediately adjacent thereto. The data is stored or written to the magnetic media by switching the direction of flow in an otherwise substantially constant magnitude write current that is established in coil windings in the write transducer in accordance with the data. Each write current direction transition results in a reversal of the magnetization direction, in that portion of the magnetic media just then passing by the transducer during this directional switching of the current flow, with respect to the magnetization direction in that media induced by the previous in the opposite direction.
Recovery of such recorded digital data is accomplished through positioning a retrieval, or xe2x80x9creadxe2x80x9d magnetic field-to-voltage transducer, or xe2x80x9cheadxe2x80x9d, to have the magnetic media, containing previously stored data, pass thereby. Such passing by of the media adjacent to the transducer permits the flux accompanying the magnetization reversal regions in that media either to induce a corresponding voltage pulse in forming an analog output read signal for that retrieval transducer or, alternatively, change a transducer circuit parameter based on magnetoresistive sensing of magnetic conditions therein to thereby provide such an output signal voltage pulse.
Such transducers or sensors can often be advantageously fabricated using ferromagnetic thin-film materials. Ferromagnetic thin-film sensors can be made very small when so constructed. Such sensors are often provided in the form of an intermediate separating material having two major surfaces on each of which an anisotropic ferromagnetic thin-film is provided. In such xe2x80x9csandwichxe2x80x9d structures, reducing the thickness of the ferromagnetic thin-films in the intermediate layer has been shown to lead to a xe2x80x9cgiant magnetoresistive effectxe2x80x9d being present for an electrically conductive material intermediate layer or a xe2x80x9cspin dependent tunneling effectxe2x80x9d being present for an electrically insulative material intermediate layer. This effect can be enhanced by having additional alternating ones of such films and layers, i.e. superlattices. This effect can yield a magnetoresistive response which can be in the range of up to an order of magnitude greater than that due to the well-known anisotropic magnetoresistive response.
In the ordinary anisotropic magnetoresistive response in ferromagnetic thin-films, varying differences between the direction of the magnetization vector in such a thin-film and the direction of a sensing current passed through that film in turn lead to varying differences in the effective electrical resistance of the film in the direction of the current. The maximum electrical resistance occurs when the magnetization vector in the film and the current direction are parallel to one another, while the minimum resistance occurs when they are perpendicular to one another. The total electrical resistance of such a magnetoresistive ferromagnetic thin-film exhibiting this response can be shown to be given by a constant value, representing the minimum resistance present, plus an additional value depending on the angle between the current direction in the film and the magnetization vector therein. This additional resistance follows a square of the cosine of that angle.
As a result, external magnetic fields supplied for operating a film sensor of this sort can be used to vary the angle of the magnetization vector in such a film portion with respect to the easy axis of that film portion. This axis exists in the film because of an anisotropy present therein typically resulting from depositing the film in the presence of an externally supplied magnetic field during deposition of the film that is oriented in the plane of the film along the direction desired for the easy axis in the resulting film. During subsequent operation of a sensing device using this resulting film, such externally supplied magnetic fields for operating the film sensor can vary the magnetization vector angle to such an extent as to cause switching of that film""s magnetization vector between two stable states which occur as magnetizations oriented in opposite directions along the established easy axis. The state of the magnetization vector in such a film portion can be measured, or sensed, by the change in resistance encountered by a current directed through this film portion.
In contrast to this arrangement, resistance in the plane of either of the ferromagnetic thin-films in the xe2x80x9csandwichxe2x80x9d structure is isotropic with respect to the giant magnetoresistive effect rather than depending on the direction of a sensing current therethrough as for the anisotropic magnetoresistive effect. The giant magnetoresistive effect has a magnetization dependent component to resistance that varies as the cosine of the angle between the magnetizations in the two ferromagnetic thin-films on either side of the intermediate layer. In the giant magnetoresistive effect, the electrical resistance through the xe2x80x9csandwichxe2x80x9d or superlattice is lower if the magnetizations in the two separated ferromagnetic thin-films are parallel than it is if these magnetizations are antiparallel, i.e. oriented in opposing directions. Further, the anisotropic magnetoresistive effect in very thin films is considerably reduced from the bulk values therefor in thicker films due to surface scattering, whereas very thin films are a fundamental requirement to obtain a significant giant magnetoresistive effect. The total electrical resistance in such a magnetoresistive ferromagnetic thin-film xe2x80x9csandwichxe2x80x9d structure can be shown again to be given by a constant value, representing the minimum resistance present, plus an additional value depending on the angle between the magnetization vectors and the two films as indicated above.
Another magnetic field sensor suited for fabrication with dimensions of a few microns or less can be fabricated that provides a suitable response to the presence of external magnetic fields and low power dissipation by substituting an electrical insulator for a conductor in the nonmagnetic layer. This sensor can be fabricated using ferromagnetic thin-film materials of similar or different kinds in each of the outer magnetic films provided in a xe2x80x9csandwichxe2x80x9d structure on either side of an intermediate nonmagnetic layer which ferromagnetic films maybe composite films, but this insulating intermediate nonmagnetic layer conducts electrical current therethrough based primarily on a quantum electrodynamic effect xe2x80x9ctunnelingxe2x80x9d current.
This xe2x80x9ctunnelingxe2x80x9d current has a magnitude dependence on the angle between the magnetization vectors in each of the ferromagnetic layers on either side of the intermediate layer due to the transmission barrier provided by this intermediate layer depending on the degree of matching of the spin polarizations of the electrons tunneling therethrough with the spin polarizations of the conduction electrons in the ferromagnetic layers, the latter being set by the layer magnetization directions to provide a xe2x80x9cmagnetic valve effectxe2x80x9d. Such an effect results in an effective resistance, or conductance, characterizing this intermediate layer with respect to the xe2x80x9ctunnelingxe2x80x9d current therethrough.
In addition, shape anisotropy is often used in such a sensor to provide different coercivities in the two ferromagnetic layers, and by forming one of the ferromagnetic layers to be thicker than the other. Such devices may be provided on a surface of a monolithic integrated circuit to thereby allow providing convenient electrical connections between each such sensor device and the operating circuitry therefor.
A xe2x80x9csandwichxe2x80x9d structure for such a sensor, based on having an intermediate thin layer of a nonmagnetic, dielectric separating material with two major surfaces on each of which a anisotropic ferromagnetic thin-film is positioned, exhibits the xe2x80x9cmagnetic valve effectxe2x80x9d if the materials for the ferromagnetic thin-films and the intermediate layers are properly selected and have sufficiently small thicknesses. The resulting xe2x80x9cmagnetic valve effectxe2x80x9d can yield a response which can be several times in magnitude greater than that due to the xe2x80x9cgiant magnetoresistive effectxe2x80x9d in a similar sized sensor structure.
One common magnetic field sensing situation is the sensing of magnetization changes along a data recording track selected from many such tracks in the magnetic media of a magnetic data storage system. As these tracks are made narrower and narrower to permit increases in the data density in the magnetic media, inductive sensing of the magnetization changes along any of those tracks becomes less feasible. The smaller magnetization volumes lead to smaller outputs from an inductive sensor, and there is a limit to the number of turns in the coil used in such a sensor which can be provided to increase the output signal. Even in thin-film versions thereof, such inductive sensing structures remain relatively thick which becomes a problem as the tracks are made more narrow. Thus, sensing of the magnetization changes along the track using thin-film magnetoresistive sensors has become attractive.
Such magnetoresistive sensors for detecting magnetization changes along a track in the magnetic media are typically formed with the magnetoresistive sensor film in a rectangular shape, and sensors based on such films in initial designs therefor had such a sensing film positioned between a pair of highly permeable magnetic material shielding poles with a long side of the film""s rectangular shape located adjacent the magnetic media to result in what is oftentimes termed a horizontal sensor. More recently, such magnetoresistive sensors have had an alternative construction with such sensing films positioned between the poles with the short side of the rectangle adjacent the magnetic media to form what is often termed a vertical sensor or an xe2x80x9cend-onxe2x80x9d sensor. These kinds of sensors were both initially based on use of the anisotropic magnetoresistive effect in the sensing films. This effect gives a maximum change in magnetoresistance due to the sensed magnetic fields on the order of 2.5% at room temperature.
As data tracks in the magnetic media grow ever thinner coupled with use of higher densities of magnetization direction changes therealong, the need for a more efficient converter of such magnetization changes in the magnetic medium into a sufficiently large current or voltage output signal becomes greater. Hence, horizontal and vertical magnetoresistive sensors based on the xe2x80x9cgiant magnetoresistive effectxe2x80x9d and the xe2x80x9cspin dependent tunneling effectxe2x80x9d were introduced because of the greater changes in resistance possible from corresponding changes in externally applied magnetic fields. A vertical or end-on magnetoresistive sensor based on the xe2x80x9cgiant magnetoresistive effectxe2x80x9d or on the xe2x80x9cspin dependent tunneling effectxe2x80x9d is typically formed with a nonmagnetic intermediate conductive metal layer in the first instance, or with a nonmagnetic intermediate insulative oxide layer in the second instance, having ferromagnetic layers on opposite sides of the major surfaces thereof with all layers in corresponding rectangular shapes. As before, such a vertical sensor is mounted typically between a pair of ferromagnetic material shielding poles in a narrow gap provided therebetween so that a short side edge of the rectangular film sensor is positioned adjacent the magnetic media approximately in a plane with the sides of the poles also being positioned adjacent the magnetic media with the resultant surface in this plane forming the air bearing surface. Thus, the long sides of the sensor extend inward into the gap between the poles and away from the magnetic media.
Currently, read head transducers are typically provided as hybrid assemblies with the magnetic sensor and the sensor operating circuitry provided on one substrate mounted on the slider arm and the input signal amplifier provided as a separate integrated circuit chip mounted nearby. However, the parasitic capacitance in such an arrangement shunts away more and more of the sensor signal as the data recovery rate is increased leading to higher frequencies being present in the sensor signal. This situation can be improved by building the sensor and its operating circuitry on the input amplifier integrated circuit mounted on the slider arm so that the distance between the sensor output and the amplifier input is smaller thereby lessening the parasitic capacitance associated with that interconnection. One such arrangement is described in an earlier filed co-pending application by J. M. Daughton and Arthur V. Pohm entitled xe2x80x9cMagnetic Field Sensor With A Plurality Of Magnetoresistive Thin-film Layers Having An End At A Common Surfacexe2x80x9d having Ser. No. 08/907,561 which is assigned to the same or successor assignee as the present application and is hereby incorporated herein by reference.
Magnetoresistive xe2x80x9creadxe2x80x9d sensing structures are made very small to be in accord with the dimensions of the data tracks in the magnetic media from which they are to sense magnetization transitions, and therefore are usually made using monolithic integrated circuit fabrication techniques anyway along with other related thin-film fabrication techniques. Such limited sensing structure sizes and such limited track widths also limit the magnitude of the sensing structure output signal. However, because magnetoresistive sensing structures are to be used with increasingly narrow data tracks in the magnetic media passing by them, an increase in the number of such structures provided side by side may not feasible even though such a plurality of magnetoresistive sensing structures would be most conveniently provided in this manner because of structure sizes. This follows because in that circumstance the steps performed in using monolithic integrated circuit fabrication techniques to provide the plurality of such sensing structures would be just those used to provide one such structure as they are all fabricated simultaneously. Thus, there is desired a sensor configuration which can yield a suitable output signal for a given externally applied input signal without resulting in widening the vertical sensor or sensor portion which would limit the narrowness permitted for tracks in the magnetic media.
The present invention provides plural magnetic field sensing structures in a monolithic integrated circuit chip structure for providing at outputs thereof representations of magnetic field changes provided therein by corresponding sources of such magnetic field changes having poled pair structures with a gap space between them adjacent to which are ones of the plurality of magnetic field sensing structures. These sensing structures are formed of a plurality of magnetoresistive, anisotropic, ferromagnetic thin-film layers at least two of which are separated from one another by a nonmagnetic electrically conductive or insulative layer positioned between them, and at least one of them is interconnected with a circuit formed in the monolithic integrated circuit chip such as an amplifier. The paired pole structures may intersect a surface of the chip perpendicular to the major surfaces thereof or one of, or a surface parallel to, the major surfaces thereof. A magnetic field generating structure may also be included in the chip.